Dedicated Left Turn Lanes

cgarlick · Nov 10, 2000

This might seem like a bizarre question. When one analyze/compare volumes of a single left dedicated turn lane with dual left turn lanes, do you
consider a friction factor that is caused when people take the turn at the same time?

Initially you would think that increasing one lane to two lanes would double capacity. However, is this really true is the average speed is that the turn is made is less b/c there is a shy factor with the adjacent car making the
turn simultaneously? Or is this not significant?

teeman · Nov 21, 2000

We have a number of dual left turn lanes in operation. We delineate the turning path between them with a dotted line to clarify the turning lanes thru the intersection. I haven't noticed a "shy" factor, motorists seem to make the turn with no problem.

The lanes don't really double your left turn capacity, because the lane utilization isn't balanced, but, they allow more traffic to get through during the same time.

COLDAVE · Nov 28, 2000

We recently installed dual lefts at busy intersections in a river town. The back-up into and consequent lane closure of the adjacent through lane was eliminated.

I do not see any shy distance or speed reduction from adjacent turning vehicles. I do note that many prefer the outside lane rather than the median lane when alone at the stop bar.

Doubling the capacity would be wonderful but the extra travel distance for the outside lane does reduce the number that can clear during any cycle. We estimate a 67% increase in capacity.

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Dedicated Left Turn Lanes

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